Field of the Invention
The present invention relates to a control device for a hybrid vehicle to which an engine and a motor-generator are provided as sources of drive power.
Description of the Related Art
A hybrid vehicle is per se known in which a dog clutch DC3 and a one-way clutch OC3 are provided between a rotor shaft of a first motor-generator MG1 and a case C of a hybrid transaxle, and in which one engagement member of the dog clutch DC3 is connected to the one-way clutch OC3 while the other engagement member of the dog clutch DC3 is fixed to the case C (refer to Japanese patent No. 5120650 (JP-B-5120650)). With this type of hybrid vehicle, by controlling the dog clutch DC3 to be in its engaged state during high speed traveling, a state is established in which, due to the one-way clutch OC3, positive rotation of the first motor-generator MG1 is prevented while negative rotation of the first motor-generator MG1 is permitted. Since, due to this, a Hi gear locked mode which is a parallel mode to the high speed stage (Hi) is implemented, accordingly it is possible to enhance the energy efficiency during high speed traveling.
Moreover, a selectable one-way clutch is per se known that is capable of selecting either a locked mode in which, during rotation, it permits transmission of torque between two members only in a predetermined single rotational direction, or a free mode in which, during rotation, it separates transmission of torque in both directions between those two members (refer, for example, to Japanese Patent Application Publication No. 2011-169344 (JP-A-2011-169344)). Furthermore, Japanese Patent Application Publication No. 2004-345527 may be considered to have some relevance to the present invention.
Since this type of selectable one-way clutch is endowed with this type of function, accordingly it is possible to replace the dog clutch DC3 and the one-way clutch OC3 of the above described hybrid vehicle of JP-B-5120650 with such a selectable one-way clutch, which is a unitary device. In detail, it is possible to make such a selectable one-way clutch function in a similar manner to the drive device of JP-B-5120650 by fixing one of its two members to the case C, which thus serves as a fixed member, while connecting the other of the two members to the rotor shaft of the first motor-generator MG1, which thus serves as a rotating member.
In a hybrid vehicle in which the replacement described above has been performed, the rotating member of the selectable one-way clutch receives and bears the reaction torque of the engine torque outputted by the engine. Due to this, when the selectable one-way clutch is in the locked mode and thus in the state in which positive rotation of the rotating member is prevented, the state in which torque acts upon the rotating member in the positive direction continues.
However, when this hybrid vehicle travels over a road surface such as a wavelike road in which concave and convex irregularities are repeated periodically, such as a so called “wavelike road”, the torque upon the output portion changes quasi periodically due to repeated increases and reductions of rotational speed being inputted from the drive wheels. Due to this periodic variation, when the rotational speed of the wheels drops, the torque of the output portion acts in the direction to reduce the engine rotational speed, and the engine rotational speed drops. And next, when the rotational speed of the wheels increases, although the torque of the output portion acts in the direction to increase the engine rotational speed, due to the inertia of the engine, the engine rotational speed does not rise immediately. Because of this, sometimes it happens that the torque upon the rotating member of the selectable one-way clutch is eliminated so that the engagement of the selectable one-way clutch is temporarily released and it rotates in reverse, and, when thereafter the engine rotational speed rises, this engagement which has been temporarily released is re-engaged. Due to this, depending upon the value of the engine torque during this re-engagement, there is a possibility that some component of the selectable one-way clutch may be damaged when its re-engagement occurs at a rotational speed that is higher than normal. Moreover, there is a possibility that wear or strange noise may be generated due to the occurrence of ratcheting, which is a phenomenon in which, without the engagement that was temporarily released being properly re-engaged, the rotating member rotates in the positive rotational direction which is the direction in which it is not supposed to rotate.
Accordingly, an object of the present invention is to provide a control device for a hybrid vehicle which, in a traveling state in which the torque of the output portion changes periodically due to varying input to the drive wheels from the road surface over which the vehicle is traveling, is capable of suppressing deterioration of components of a selectable one-way clutch and the generation of wear or strange noise due to the occurrence of ratcheting.